The enhanced modulation of key bone matrix components by modified Titanium implant surfaces

Modifications to Titanium (Ti) implant surfaces enhance osseointegration by promoting bone-implant contact and peri-implant bone accrual; which in vitro analyses of osteoblastic cells suggest is due to an enhancement in cellular phenotypic maturation and function. To evaluate these effects on uncommitted cells, this study examined the osteogenic mineralisation and phenotypic marker expression of human marrow derived stromal cells (hBMSCs) from three unrelated donors cultured on tissue culture plastic (TCP), polished (P), rough-hydrophobic (SLA) and rough-hydrophilic (modSLA) Ti surfaces over the course of 21 days. Transcriptional analyses indicated a significant early up-regulation of both Runx2 (p<0.05) and Osteopontin (OP) (p<0.05) but not Bone Sialoprotein 2 (BSP2) (p<0.05) by rough surfaces 1 day post seeding. The phenotypic analyses showed that whilst cellular proliferation was relatively restricted and slower on the rough substrates; osteogenic mineralisation, assessed by quantifying extracellular matrix calcium deposition, collagen formation and the ratio of collagen to mineral deposited were significantly higher (p<0.05); as was alkaline phosphatase (ALP) activity (p<0.05). The rough surfaces caused an increase of secreted osteoblastic markers Osteoprotegrin (OPG) (p<0.05), growth differentiation factor 15 (GDF-15) (p<0.05) and Osteocalcin (OC) (p<0.05). These findings suggest that modified Ti surfaces induce an enhancement in osteogenic commitment and differentiation, which likely underlie the deposition of more stable bone matrix early in the healing process in vivo.